Definition
A precision approach and landing guidance system that uses microwave signals to provide aircraft with accurate azimuth (lateral), elevation (vertical), and range information during the final approach to a runway. MLS was developed as a more flexible alternative to ILS, supporting curved and segmented approaches and offering better performance in terrain that can disrupt ILS signals. In current U.S. operations, MLS is largely historical and has been displaced by GPS-based and ILS approaches, but it still appears in regulatory text and inoperative-components tables.
Plain English
A landing guidance system that uses microwave radio signals to tell the aircraft where the runway is, both side-to-side and up-and-down, so the pilot can fly an accurate approach.
Context Anchor
Seen in instrument approach and aircraft equipment discussions, especially when checking whether a required landing-system component is working or inoperative.
Derivation
Microwave refers to a band of very short-wavelength radio waves (much shorter than those used by ILS). Using microwaves allowed the system to send narrower, more precise guidance beams and to be sited in places where ILS signals would be distorted by buildings or terrain.
Why Pilots Care
Offers more flexible approach paths than ILS and works at airports where terrain limits conventional systems, improving safety during low-visibility landings.
Intuition Check
Do not read “microwave” as heat or an oven. In MLS, it means radio signals used for landing guidance.
Example Sentence 1
The inoperative components table lists separate substitution values for ILS and MLS approaches.
Example Sentence 2
MLS allowed a curved approach path that avoided high terrain east of the airport.